Dual pump system and control valve assembly therefor



Sept. 1, 1964 H. J. STACEY 3,146,593

DUAL PUMP SYSTEM AND CONTROL VALVE ASSEMBLY THEREFOR Filed April 18, 1960 2 Sheets-Sheet 1 FIG. 1

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DUAL. PUMP SYSTEM AND CONTROL VALVE ASSEMBLY THEREFOR Filed April 18, 1960 I 2 Sheets-Sheet 2 \o 2 gm m m a g F g 9* g *2 (\l m I 2 g m IL- a I [LI g Q I f 1f! 7-2 5 l m gm /|'2 F F p 8 F 0 E4 3 3 h N\ fi "$2 INVENTOR.

HUGH J. STACEY ATTORNEYS United States Patent DUAL PUMP SYSTEM AND CONTROL VALVE ASSEMBLY THEREFOR Hugh J. Stacey, Chester-land, Ohio, assignor to Parker- Hannifin Corporation, Cleveland, Ohio, a corporation of Ohio Filed Apr. 18, 196i), Ser. No. 23,036 15 Claims. (Cl. 60-62) The present invention relates generally as indicated to a dual pump system and control valve assembly therefor, and more particularly, to such system and valve assembly for use with a backhoe and like equipment that employs a plurality of fluid motors desired to be operated at high speeds under light or moderate loads and at low speeds but high fluid pressures, under heavy loads.

In equipment of the character referred to wherein the components are hydraulically actuated there are usually provided: (1) a plurality of large capacity hydraulic motors e.g. for raising and lowering the boom thereof, for swinging the crowd arm toward or away from the tractor, and for moving the scoop or bucket mounted on the crowd arm to digging and dump positions; and (2) a plurality of small capacity hydraulic motors e.g. for moving the stabilizers or out-riggers of the tractor to and from ground-engaging position, and for swinging the boomcrowd arm-scoop assembly about a vertical axis. As evident, these small capacity hydraulic motors for operating auxiliaries, such as the stabilizers, are not used to any great extent during the principal operation of the machine and therefore their actuation is amply satisfied by a small capacity-high pressure pump. However, as to the large capacity hydraulic motors it is desired to operate the components with which they are associated at high speeds i.e. by a large capacity-lower pressure pump when lightly loaded and at low speeds and high pressure i.e. by a small capacity pump when such components encounter substantial obstructing forces.

Accordingly, to best satisfy the foregoing requirements it is a principal object of this invention to provide a dual pump system and control valve assembly which has a large capacity pump for supplying fluid through the control valve assembly for operating the large capacity hydraulic motors at desired high speeds when under light or moderate loads; a small capacity pump for feeding either to the large capacity motors (to supplement the large capacity pump) or in lieu thereof or to the small capacity motors via said control valve assembly; an unloader for the large capacity pump operative to dump its discharge back to the tank whenever the large capacity motors encounter substantial loads which can amply be overcome solely by the feed of the small capacity pump at reduced speed; and a bypass arrangement in the control valve assembly effective to freely bypass the discharge of both pumps back to the tank when none of the motors are being actuated.

It is another object of this invention to provide a dual pump system and control valve assembly which is arranged so that any or all of the motors may be actuated without interflow of fluid between two or more motors that are at the same time operating under different loads.

It is another object of this invention to provide a dual pump system and control valve assembly in which the large capacity circuit has its own bypass arrangement to the tank when none of the large capacity motors is in operation and to which the bypass arrangement of the small capacity circuit is joined for free bypass of its discharge to the tank via the large capacity bypass when none of the small capacity motors is in operation.

It is another object of this invention to provide a dual pump system and control valve assembly in which the 3,146,593 Patented Sept. 1, 1964 aforesaid bypass of the large capacity circuit is closed and becomes the large capacity feed whenever any of the large capacity motors are in operation, in which case, the aforesaid bypass of the small capacity circuit becomes a supplemental pressure feed to augment the large capacity circuit.

It is another object of this invention to provide a dual pump system and control valve assembly in which the bypass of the small capacity circuit is closed and becomes the pressure feed to the small capacity motors whenever any of said small capacity motors are in operation.

It is another object of this invention to provide a dual pump system and control valve assembly in which the unloader aforesaid is formed as a part of the valve assembly and is arranged to unload the large capacity pump whenever the conjoint pressure feed of both pumps to any of the large capacity motors exceeds a predetermined maximum pressure at which it is desired to unload the large capacity pump while continuing high pressure actuation of said large capacity motors at lower speed.

It is another object of this invention to provide a simple and compact control valve assembly for a dual pump system which has directional control valves and paired service ports for connection to the respective large and small capacity motors, pressure inlet ports for connection to the respective large and small capacity pumps, a tank port for connecting the common portion of the bypasses of the large and small capacity circuits to the tank, an unloader for the large capacity circuit, and load checks upstream of the respective directional control valves operative to prevent backflow or interflow of fluid when two or more motors are simultaneously operated under different loads.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principle of the invention may be employed.

In said annexed drawings:

FIG. 1 is a schematic side elevation view of a typical backhoe showing the locations of the several hydraulic motors which are required to perform various operations such as actuating the stabilizers on opposite sides of the tractor, swinging the boom about a vertical axis, raising and lowering the boom about a horizontal axis, swinging the crowd arm toward and way from the tractor, and tilting the bucket or scoop to digging and dumping positions, the fluid tank or reservoir, the fluid lines, the dual pump and the control valve assembly being shown schematically without regard to their actual locations on the tractor proper; and

FIG. 2 is another schematic diagram showing the control valve assembly in cross-section in a plane passing through the axes of the parallel banks of spool-type large and small capacity directional control valves therein and through other components of said valve assembly, the hydraulic motors and their connections to the paired service ports of the valve assembly being omitted for sake of clarity, but being apparent from FIG. 1.

Referring now more particularly to the drawings and first to FIG. 1 the backhoe 1 herein shown by way of illustrative example only, comprises an engine-driven tractor 2 having front and rear wheels 3 and 4 and the usual steering wheel 5 and drivers seat 6. On opposite sides of the tractor 2 are stabilizers 7 and S (hydraulic motors) a which are mounted in outwardly and downwardly inclined positions so that, when extended, the respective floats 9 and 10 thereof are pressed against the ground to provide added lateral stability to the tractor against tipping and to preclude excessive loads on the wheels 3 and 4 and their supporting axles. Mounted on the rear end of the tractor 2 for swinging about the vertical axis of the gudgeon 11 is the boom assembly comprising the boom 12 which has its foot pivoted at 14 about a horizontal axis, the crowd arm 15 which is pivoted at 16 to the boom tip, and the scoop or bucket 17 which is tiltable at 18 with respect to the crowd arm 15 between digging and dumping positions.

The foregoing components are arranged for selective actuation by the several hydraulic motors 7 and 8 (stabilizer cylinders), 19 (swing cylinder), 20 (boom hoisting and lowering cylinder), 21 (crowd arm cylinder), and 22 (bucket cylinder) in a manner which is self-evident in FIG. 1.

As known in the art, large capacity pumps operate at maximum efiiciency when used to deliver a large volume of fluid to a hydraulic motor at low pressure for rapid actuation of the motor when lightly loaded, and small capacity pumps operate at maximum efliciency when used to deliver a small volume of fluid to a hydraulic motor at high pressure for intensified, slow actuation of the motor when heavily loaded. In a backhoe 1 and like machine, the stabilizers and swing assembly may be considered to be auxiliaries which, when once set or actuated, are not generally used during the principal operations of the machine such as the raising and lowering of the boom 12, the moving of the crowd arm 15 toward and away from the tractor 2, and the tilting of the bucket 17 between digging and dumping positions. Accordingly, the stabilizer motors 7 and 8, and the swing motor 19 may be so-called small capacity motors adapted for separate or simultaneous actuation by a small capacity pump 23, whereas, the boom motor 20, the crowd arm motor 21, and the bucket motor 22 perform the principal functions of the machine and preferably are so-called large capacity motors adapted, when lightly loaded, for separate or simultaneous high speed actuation by the conjoint discharge of small and large capacity pumps 23 and 24 and, when heavily loaded, for separate or simultaneous low speed actuation by the small capacity pump 23 alone.

The control valve assembly 25 as herein shown comprises a unitary housing 26 including a bank 27 of small capacity directional control valves 28, 29, and 30 for the respective swing and stabilizer motors 19, 7, and 8. As shown in FIG. 1, conduits 31; 31, 32; 32, and 33; 33 interconnect the respective motors 19, 7, and 8 with corresponding paired service ports of the respective directional control valves 28, 29, and 30. Similarly, there is in the housing 26 a bank 37 of large capacity directional control valves 38, 39, and 40 for the respective boom, crowd arm, and bucket motors 20, 21, and 22. Again as shown in FIG. 1, conduits 41; 41, 42; 42, and 43; 43 interconnect the respective motors 20, 21, and 22 with corresponding paired service ports of the respective directional control valves 38, 39, and 40. Thus by manipulating the directional control valves 28, 29, and 30 and 38, 39, and 40 by suitable levers (not shown) the respective motors 19, 7, and 8 and 20, 21, and 22 may be extended or retracted, as desired.

The housing 26 is formed with a small capacity inlet port to which the conduit 50 is connected from the delivery port of the small capacity pump 23, a large capacity inlet port to which the conduit 51 is connected from the delivery port of the large capacity pump 24, and a tank port communicated by way of conduit 52 to tank 53. Of course, conduit 54 is provided for flow of fluid from tank 53 into the intake ports of pumps 23 and 24.

It is to be understood that the pumps 23 and 24 may be combined as a dual pump having a single drive shaft 55 suitably coupled to the tractor engine (not shown), that the tank 53 will be mounted in some convenient place on the tractor 2, that the valve assembly 25 similarly will be mounted on the tractor 2 so that its directional control valve levers (not shown) may be manipulated by the operator when seated on the tractor seat 6, and that various conduits will comprise tubes and flexible hoses and will be concealed when possible so as not to interfere With or to be damaged by operation of the machine.

Having thus described the dual pump system as a whole as shown in FIG. 1, reference will now be made to FIG. 2 which illustrates the valve assembly 25 in detail.

The banks 27 and 37 of small capacity directional control valves 28, 29 and 30 and large capacity directional control valves 38, 39, and 4% are, as aforesaid, a part of the housing 26, and preferably the valves 28, 29, and 30 and 38, 39, and 40 are spool type valves although they may be of the rotary type, poppet type, or equivalent type which may be manipulated to extend or retract hydraulic cylinders.

he valve housing 26, when formed to accommodate spool type directional control valves 28, 29, 30, 38, 39, and 40, is preferably formed with a corresponding number of parallel bores for said spools, each spool having at one end, a spring return mechanism 60 of familiar form. For four-way spools 28, 29, 30, 38, 39, and 40 as herein shown by way of example each spool will have a center neutral position in its bore from which it is adapted to be shifted axially in one direction or the other according to whether the associated hydraulic motor is to be extended or retracted. Intersecting the parallel bores of the spools 28, 29, and 30 of the small capacity bank 27 and also the parallel bores of the spools 33, 39, and 40 of the large capacity bank 37 are:

(l) A central bypass 61 which leads from the inlet port 62 of bank 27 through check valve 63, and through the central bypass 64 of bank 37 to the tank port 65, such bypasses 61 and 64 being open when all of the spools 28, 29, and 30, and 38, 39, and 40 are in neutral position, as shown, whereby the delivery of the small capacity pump 23 flows freely to the tank 53 via conduit 50, inlet port 62, bypass 61, check valve 63, bypass 64, tank port 65, and conduit 52; and similarly the delivery of the large capacity pump 24 is bypassed to the tank 53 (when all spools 38, 39, and 40 are in neutral) via conduit 51, inlet port 67, check valve 68, bypass 64, tank port 65, and conduit 52;

(2) Parallel pressure branches 69 and 70 associated with the banks 27 and 37 and common to the inlet ports 62 and 67 respectively and straddling the respective bypasses 61 and 64;

(3) Pressure feed branches 71 and 72 straddling the respective branches 69 and '70 and leading from the latter via individual check valves 73 and 74 to the respective spools of banks 27 and 37;

(4) Service ports 75 and 76 straddling the respective feed branches 71 and 72; and

(5) Return passages 77 and 78 common to banks 27 and 28 straddling the service ports 75 and 76, there being a relief valve 79 between inlet port 62 and one return passage 77 and an unloader 80 between inlet port 67 and one return passage 78, and, in addition, the unloader 80 has a pressure actuator 81 exposed to fluid pressure in the inlet port 67 on the downstream sides of check valves 63 and 68.

The spools 28, 29, and 3t) and 38, 39, and 40 are formed with alternate lands and grooves so that when any one of them is shifted axially from neutral, its associated bypass 61 or 64 is blocked so that pressure builds up in the inlet port 62 or 67 and pressure branches 69 or 70 passes through a selected service port 75 and 76 to extend or retract the associated hydraulic motor. In the present system, the spools are arranged in parallel so that any one, two, three, four, five, or six may be simultaneously actuated to control the direction of actuation of the associated motors. However, if all of the small capacity -spools 28 29, and 30 are in neutral position, while one or more of the large capacity spools 38, 39 and 40 are actuated then the selected motors (when under light load) will be rapidly actuated by the combined delivery of both pumps 23 and 24 because in that event, the discharge from pump 23 will flow through bypass 61 and check valve 63 into the inlet port 67 (bypass 64 blocked by the one or more of the shifted spools 38, 39, and 40).

On the other hand, when the large capacity motor or motors encounter a substantial load or obstruction the pressure in the inlet port 67 acting on the end of the unloader actuator 81 will build up sufliciently to move the unloader valve member 82 down against spring 83. This will cause the discharge of large capacity pump 24 to be dumped into return passage 78 to relieve the load on pump 24. When that occurs, the pump 23 alone will continue to supply the high pressure needs of the heavily loaded large capacity motor or motors but at reduced speed. The relief valve 79, of course, will be set for a somewhat higher pressure than required for unloading as aforesaid to relieve the pump 23 from overload in the event either of an excessively heavy load on the large capacity motor or its piston reaching the end of its stroke.

The check valves 73 and 74 are commonly referred to as load checks preclude interflow or back flow of fluid from a heavily loaded motor to a less heavily loaded motor when two or more motors are simultaneously actuated. The check valve 63 prevents flow of fluid from the large capacity bank 37 to the small capacity bank and the check valve 68 prevents release of pressure in the large capacity bank 37 when supplied by the small capacity pump 23 while the large capacity pump 24 is being unloaded by unloader 80.

Having thus described a preferred embodiment of this invention in detail it can be seen that I have provided a dual pump system and control valve assembly that fulfills all of the aforesaid stated objects of this invention and, especially, utilizes large and small capacity pumps to their best advantages and in a unique manner for conjoint low pressure, rapid actuation of large capacity motors, for relatively rapid and high pressure actuation of small capacity motors solely by the small capacity pump, and for high pressure, slow actuation of large capacity motors, when heavily loaded, solely by the small capacity pump while the large capacity pump is unloaded.

It is to be understood that the directional control valves may be variously modified and that the passages in housing 26 may be rearranged for series operation of motors or for series-parallel operation instead of parallel operation as herein shown.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A fluid power system comprising at least two fluid pressure operated units with associated control valves and pumps arranged so that said units may be operated by fluid under pressure delivered by the respective pumps, and so that one unit may be operated by the conjoint discharge of both pumps only when the other unit is not in operation; an unloader for the pump associated with said one unit operative to unload that pump when the fluid pressure delivered to said one unit exceeds a predetermined value; a first check valve downstream of said unloader for maintaining such fluid pressure to said one unit while said one pump is unloaded; and a second check valve between said units permitting flow of fluid under pressure from the other pump to said one unit for continued operation of the latter.

2. The system of claim 1 wherein said unloader comprises a fluid pressure actuated member that is exposed to fluid pressure delivered to said one unit by its associated pump via said first check valve, by both pumps via said first and second check valves, and by said other pump via said second check valve.

3. The system of claim 1 wherein the control valve for said one unit has a bypass passage which is common to the bypass passage of the other control valve for bypassing the discharge of both pumps when neither unit is in operation.

4. A fluid power system comprising two banks of fluid pressure operated units with associated banks of control valves and two pumps arranged so that the units of the respective banks may be operated separately or concurrently by fluid under pressure delivered by the respective pumps, and so that the units of one bank may be operated separately or concurrently by the conjoint discharge of both pumps only when the units of the other bank are not in operation; an unloader for the pump associated with the units of said one bank operative to unload that pump when the fluid pressure delivered to any of the units of said one bank exceeds a predetermined value; a first check valve downstream of said unloader for maintaining such fluid pressure to the units of said one bank while said one pump is unloaded; and a second check valve between said banks permitting flow of fluid under pressure from the other pump to the units of said one bank for continued operation of one or more of the last-mentioned units.

5. The system of claim 4 wherein said unloader comprises a fluid pressure actuated member that is exposed to fluid pressure delivered to said one bank by its associated pump via said first check valve, by both pumps via said first and second check valves, and by said other pump via said second check valve.

6. The system of claim 4 wherein the control valves for the units of said one bank have a bypass passage which is common to the bypass passage of the control valves for the units of said other bank for bypassing the discharge of both pumps when none of the units of either bank are in operation.

7. A directional control valve assembly for control ling operation of two banks of fluid motors; said assembly comprising a unitary housing including therein two banks of control valve members adapted to control the fluid motors of the respective banks; said housing being formed with two inlet ports adapted for connection with two different fluid pressure sources, with two banks of pressure feed passages communicating with the respective inlet ports, and with service ports associated with the respective control valve members and adapted for connection with the respective fluid motors of said banks; said control valve members being movable in said housing to communicate the respective inlet ports and feed passages with said service ports to control actuation of the associated fluid motors; said housing being formed with two bypass passages that are joined together for flow of fluid from both inlet ports through one of said bypass passages when all of said control valve members are in positions blocking communication between said inlet ports and said service ports; an unloader for the inlet port of one bank of control valve members operative to unload said inlet port when the fluid pressure therein and in the pressure feed passages as occasioned by such movement of any of the control valve members of said one bank exceeds a predetermined value; a first check valve in said housing downstream of said unloader for maintaining such fluid pressure in the feed passages of said one bank of control valve members while said one inlet port is thus unloaded; and a second check valve between said banks permitting flow of fluid under pressure via the bypass passage of the other bank of control valve members for continued flow of fluid to the feed passages of said one bank from the other inlet port.

8. The valve assembly of claim 7 wherein said unloader comprises a fluid pressure actuated member that is exposed to fluid pressure delivered to said one bank by its associated pressure source via said first check valve, by both pressure sources via said first and second check valves, and by the other pressure source via said second check valve.

9. The valve assembly of claim 7 wherein a pressure relief valve is provided to relieve said other inlet port when the fluid pressure therein and in the feed passages or bypass passage of said other bank of control valve members exceeds a predetermined value which is greater than that which causes said unloader to unload said one inlet port.

10. A fluid power system comprising at least two fluid pressure operated units with associated control valves and pumps arranged so that said units may be operated by fluid under pressure delivered by the respective pumps, and so that one unit may be operated by the conjoint discharge of both pumps only when the other unit is not in operation; the control valve for said one unit having a bypass passage which is common to the bypass passage of the other control valve for bypassing the discharge of both pumps when neither unit is in operation; an unloader for the pump associated with said one unit operative to unload that pump when the fluid pressure delivered to said one unit via the common bypass of said one control valve exceeds a predetermined value; a first check valve downstream of said unloader for maintaining fluid pressure in said common bypass passage while said one pump is unloaded; and a second check valve between said control valves permitting flow of fluid under pressure from the other pump to said one unit via the bypass passage of said other control valve. l

11. The system of claim 10 wherein said other control valve has a pressure relief valve operative to relieve said other pump when the pressure delivered thereby either to said other unit or to said one unit exceeds a value greater than that which causes said unloader to unload said one pump.

12. In a hydraulic power transmission system, a first hydraulic pump, a first group of open center spool-type valves having a pressure side connected with said first pump, a series of hydraulic cylinders, each cylinder being connected with one of said valves for control there: by, a second hydraulic pump, a second group of open center spool-type valves having a pressure side connected with said second pump, a second series of hydraulic cylinders, each cylinder being connected with one of said second group of valves for control thereby, a pressure relief valve limiting hydraulic pressure in the pressure side of each of said groups of valves and a one-way fluid flow connection between the pressure sides of said two groups of valves, the fluid flow connection between the pressure sides of the two groups of valves being through pressure passage of one of the valves of each group, and said pressure passage being closed upon actuation of either of said valves.

13. In a hydraulic power transmission having a pair of driven pumps for actuating a plurality of hydraulic cylinders, each of said pumps having an inlet port, a selector valve comprising a housing and a plurality of valve spools in said housing selectively operable to direct fluid flow to said cylinders, ports operatively associated with said spools and passages connected with said ports forming an open center pressure distribution system, means connecting one of said pumps to one end of said open center system, means connecting the other pump to said system between certain of said spools, an unloading valve disposed in said housing between the respective pump inlet ports and operable to vent the system at preselected pressure, and a check valve disposed between said unloading valve and one of said pump inlet ports operable in response to opening of said unloading valve.

14. A hydraulic valve comprising, a housing, inlet ports and outlet ports in said housing, passages interconnecting said ports to form an open center system, movable spools associated with said passages operable when actuated to close off open center fluid flow and cause pressure build-up at an associated outlet port, a biased unloading valve disposed in said housing between certain of said spools and operable to vent a portion of the open center system, and a check valve disposed operatively adjacent said unloading valve and operable to isolate the remainder of the open center system in response to operation of said unloading valve.

15. A hydraulic valve comprising a first group of open center spool-type valves having a pressure side adapted to be connected with a first hydraulic pump, said first group of valves also being adapted to be connected to a first series of hydraulic cylinders, a second group of open center spool-type valves having a pressure side adapted to be connected to a second hydraulic pump, said second group of valves also being adapted to be connected to a second series of hydraulic cylinders, a pressure relief valve limiting hydraulic pressure in the pressure side of each of said groups of valves and a one-way fluid flow connection between the pressure sides of said two groups of valves, the fluid flow connection between the pressure sides of the two groups of valves being through a pressure passage of one of the valves of each group, and said pressure passage being closed upon actuation of either of said valves.

References Cited in the file of this patent UNITED STATES PATENTS 2,247,140 Twyman June 24, 1941 2,643,516 Carlson June 30, 1953 2,656,152 Moon Oct. 20, 1953 2,745,253 Towler et al. May 15, 1956 2,856,960 Stacey Oct. 21, 1958 

1. A FLUID POWER SYSTEM COMPRISING AT LEAST TWO FLUID PRESSURE OPERATED UNITS WITH ASSOCIATED CONTROL VALVES AND PUMPS ARRANGED SO THAT SAID UNITS MAY BE OPERATED BY FLUID UNDER PRESSURE DELIVERED BY THE RESPECTIVE PUMPS, AND SO THAT ONE UNIT MAY BE OPERATED BY THE CONJOINT DISCHARGE OF BOTH PUMPS ONLY WHEN THE OTHER UNIT IS NOT IN OPERATION; AN UNLOADER FOR THE PUMP ASSOCIATED WITH SAID ONE UNIT OPERATIVE TO UNLOAD THAT PUMP WHEN THE FLUID PRESSURE DELIVERED TO SAID ONE UNIT EXCEEDS A PREDETERMINED VALUE; A FIRST CHECK VALVE DOWNSTREAM OF SAID UNLOADER FOR MAINTAINING SUCH FLUID PRESSURE TO SAID ONE UNIT WHILE SAID ONE PUMP IS UNLOADED; AND A SECOND CHECK VALVE BETWEEN SAID UNITS PERMITTING FLOW OF FLUID UNDER PRESSURE FROM THE OTHER PUMP TO SAID ONE UNIT FOR CONTINUED OPERATION OF THE LATTER. 